When high-density mounting is required of semiconductor devices, bare chip mounting is ideal. However, a bare chip presents problems of quality assurance and handling. In response to this, semiconductor devices have been developed to which CSP (Chip Scale/Size Package) is applied. There is no formal definition of CSP, but generally it is understood to refer to an IC package with a package size the same as an IC chip, or very slightly larger than an IC chip. To advance high-density mounting, the development of CSP technology is important. As a publication of a prior art relating to CSP may be cited International Publication No. WO95/08856.
According to this document, a gap is formed between a substrate having external terminals and a semiconductor chip, and this gap is filled with resin. This resin is resilient when cured. This resilient resin absorbs stress (thermal stress) applied to the external terminals. It should be noted that this stress is generated by the difference in the coefficients of thermal expansion of the semiconductor device and the circuit board on which the semiconductor device is mounted.
However, since it is difficult to form a thick layer of the resin disposed between the semiconductor chip and the substrate, thermal stress has not been adequately absorbed.